The present invention is in the technical field of electrification systems for electrically powered railways. More particularly, the present invention is a combined synchronous and asynchronous power supply modules for control of electrically powered shuttle-trains on a track system with segmented power supply rails.
Conventional electrified railways are not deployed for the purpose of large-scale energy storage in which grid electrical energy is stored for use at an alternate time of consumption. However, an effective means for large-scale energy storage may be achieved by constructing an electrified steel railway network which employs regenerative traction drive shuttle-trains, operating on a closed low-friction automated steel rail network, to transport heavy container-sized masses between two storage yards at different elevations, converting electricity into potential energy and back into electric power as needed. In such a system when excess energy is available on the grid, the masses are transported uphill from a lower storage yard, drawing electricity from the grid to power the motors of shuttle-trains as they move the masses against the force of gravity to an upper storage yard; when the grid requires energy to meet periods of high demand, the process may be reversed, the shuttle-trains return the masses to the lower storage yard with their generators converting the potential energy of the masses back into electricity in a highly efficient process.
The present invention is intended to facilitate the use of electrified railways for energy storage by reducing the cost and improving the serviceability and efficiency of the power conversion equipment necessary to provide frequency control of the electric power governing the speed of electrified trains operating on such a system.
In a conventional alternating current electrified railway the power provided to the locomotive is of uniform voltage and frequency across the system. The speed control of the train is generally accomplished by means of onboard rectifier/inverter sets which sense the rotational speed of a locomotives drive motors and provide power to the motors at the correct alternating current frequency to power the train at a set speed or rate of speed change. In this scenario each locomotive is required to have onboard power conversion equipment capable of rectifying trackside alternating current into onboard direct current, which is then inverted back into alternating current at the frequency required by the drive motors. The cost of this onboard power conversion equipment is a significant portion of the cost of a locomotive and the electrical losses associated with rectifying and inverting the current to a trains traction drives is significant. In the case of an electrified railway deployed for energy storage the onboard rectifier/inverter units deployed in such system must be certified for interconnection to a utility grid. Electrical equipment meeting these certification requirements is far more expensive than normal locomotive power conversion systems.
It is therefore desirable to reduce the use, number and capacity of rectifier/inverter power conversion units required to power an electrified railway certified for grid interconnection as an energy storage system.